An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. Each printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors, each ejector consisting of an ink chamber, an ejecting actuator and an orifice through which droplets of ink are ejected. The ejecting actuator can be one of various types, including a heater that vaporizes some of the ink in the chamber in order to propel a droplet out of the orifice, or a piezoelectric device which changes the wall geometry of the chamber in order to generate a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other print medium (sometimes generically referred to as paper herein) in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the print medium is moved relative to the printhead.
Motion of the print medium relative to the printhead can consist of keeping the printhead stationary and advancing the print medium past the printhead while the drops are ejected. This architecture is appropriate if the nozzle array on the printhead can address the entire region of interest across the width of the print medium. Such printheads are sometimes called pagewidth printheads. A second type of printer architecture is the carriage printer, where the printhead nozzle array is somewhat smaller than the extent of the region of interest for printing on the print medium and the printhead is mounted on a carriage. In a carriage printer, the print medium is advanced a given distance along a print medium advance direction and then stopped. While the print medium is stopped, the printhead carriage is moved in a direction that is substantially perpendicular to the print medium advance direction as the drops are ejected from the nozzles. After the carriage has printed a swath of the image while traversing the print medium, the print medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath. In order to accomplish the motions necessary for printing in a carriage printer, there are typically at least two motors—the motor for print medium advance, and the motor for carriage motion. The examples described in the present invention relate to a carriage printer architecture.
Inkjet ink includes a variety of volatile and nonvolatile components including pigments or dyes, humectants, image durability enhancers, and carriers or solvents. A key consideration in ink formulation is the ability to produce high quality images on the print medium. During periods when ink is not being ejected from an ejector, the volatile components of the ink can evaporate through the nozzle, or there can be other factors why the ink properties (such as viscosity) at the nozzle can change. Such changes can make the drop ejection process nonuniform, so that the image quality can be degraded. In addition, dust, dried ink or other particulates can partially block a nozzle or make the wettability of the nozzle face around the nozzle nonuniform so that ejected drops can be misdirected from their intended flight paths.
In order to maintain the drop ejecting quality of the printhead so that high quality images are produced even after periods where one or more nozzles has been inactive, a variety of maintenance actions have been developed and are well known in the art. These maintenance actions can include capping the printhead nozzle face region during periods of nonprinting, wiping the nozzle face, periodically spitting drops from the nozzles into the cap or other reservoir that is outside the printing region, priming the nozzles by applying a suction pressure at the nozzle face, etc. In addition, in order to remove excess ink from the cap due to spitting or priming, it can be useful to pump the waste ink into a waste pad region where it can accumulate and dry over the lifetime of the printer. Although a separate motor can be used to perform one or more of the maintenance functions, low cost designs typically perform maintenance functions using the motor for print medium advance or the motor for carriage scanning. However, it can be difficult to provide the full range of maintenance functions without a separate motor. At the same time, as the requirements for high quality and long lasting images continue to be extended, a low cost design of a full function maintenance station is needed.
Motions which are typically involved for various maintenance operations can include motions of the cap, the wipers and a pump. When the printhead is done printing, the carriage is typically moved to a “home position” which is located outside the printing region. The cap is located at or near the home position, but when the carriage moves into the home position, there is a gap between the cap and the printhead face so that the two do not collide and do damage to one another. When the carriage is located in the home position, the cap is typically moved into a confronting position with the nozzle face. When the carriage gets ready to leave the home position in order for the printhead to print, the cap must again be moved away from the nozzle face.
The motion of the wiper(s) depends on whether wiping has been designed to occur along the nozzle array direction or across the nozzle array direction. FIG. 1 shows the nozzle face 252 of a printhead die 251. In this example, there are three nozzle arrays 253 that are aligned along nozzle array direction 254 and that are spaced apart from one another along a direction perpendicular to the nozzle array direction. The nozzle arrays 253 are each staggered so that the nozzle in an array are not aligned in a single line along direction 254, but rather in two lines. Typically, the nozzles of the top nozzle array in this example might eject ink of one color (such as cyan), while the nozzles of the middle nozzle array might eject ink of a second color (such as magenta), and the nozzles of the bottom nozzle array might eject ink of a third color (such as yellow). Along the nozzle array direction 254 in this direction for a given array, are disposed nozzles to eject ink of a single type. Also shown in FIG. 1 are wirebond interconnections 255 to connect electrical pads on printhead die 251 with pads at the ends of leads 259 on flex circuit 257. The wire bonds are coated with an encapsulant 256.
A perspective view of the printhead die 251 of FIG. 1 is shown in FIG. 2. The die 252 and the flex circuit 257 are mounted on supporting substrate 261. In FIG. 2, a wiper blade 112 is shown moving along nozzle array direction 254 in order to wipe away a pool of ink 270. The wiper blade can actually move the pool of ink 270 over the mound of encapsulant 256. An advantage of wiping along the nozzle array direction is that there is less likelihood of cross-contamination between the different fluids in the different nozzle arrays 253. Many printers are designed such that wiping occurs across the nozzle arrays, i.e. the respective motion between the wiper blade and the nozzle face is perpendicular to nozzle array direction 254. One reason that this is done is that the wiper blade 112 can be held in a stationary position toward the end of carriage travel and the nozzle face 252 simply brought past the wiper blade by the motion of the carriage.
As is well known in the art, the nozzle array direction 254 in a carriage printer must be substantially perpendicular to the carriage motion direction, in order to print the image. Also note that the length of the wiper blade 112 should be substantially perpendicular to the relative motion of the wiper blade 112 and the nozzle face 252. Therefore, if the relative motion of the wiper blade 112 and the nozzle face 252 is accomplished by carriage motion, the length of the wiper blade will be along nozzle direction 254, and wiping will occur from one nozzle array to the next. Examples of such systems that wipe perpendicular to the nozzle array direction are provided in U.S. Pat. No. 5,257,044, U.S. Pat. No. 5,831,644, U.S. Pat. No. 5,917,516, U.S. Pat. No. 5,971,520, U.S. Pat. No. 6,309,044, U.S. Pat. No. 6,540,320, and U.S. Pat. No. 6,991,312. In such systems, it can still be necessary to move the wipers from a retracted position to a position such that the blade can contact the nozzle face, but as wiping is occurring, the blade typically remains fixed.
On the other hand, if the wiping is to be done along the nozzle array direction, then the wipers cannot remain in a fixed position while the carriage moves the nozzle face past. Rather the wipers must be actively moved in order to wipe along the nozzle array direction. Examples of wipers that are moved along the nozzle array direction are provided in U.S. Pat. No. 6,702,424, U.S. Pat. No. 6,846,060 and U.S. Pat. No. 7,225,697.
Motion in a mechanical pump is also typically actuated in an inkjet system. This is done in order to provide a suction force in order to prime the printhead when needed, and also can be done in order to empty waste ink out of the cap. Typically, priming is done at a time when the cap is sealed up against the nozzle face of the printhead, while cap emptying is done when the cap is separated from the printhead. In many printers the type of pump that is used is a tube pump.
It can be appreciated that it is desirable to control some of the maintenance operations independently of the others. For example, it is not necessary to prime the printhead every time the printhead is capped. Furthermore, the duration of priming can need to be customized according to the ink used (i.e. different ink viscosities), the nozzle size, the environmental conditions, or the time since the last printing operation, for example. In addition it is not necessary to empty waste ink from the cap every time the cap is moved away from the nozzle face. It can also not be necessary to cap after every wiping operation. In much of the prior art, maintenance operation has its timing determined by mechanical components such as gears and cams in order to sequence the operations.
There is a need in a low cost inkjet printer for a maintenance station that a) does not require an additional motor; b) is able to perform the full set of maintenance operations of capping, wiping, priming and emptying the cap; and c) allows at least some of the maintenance operations to be controlled independently—such as whether or not to pump and how long to pump to accommodate different printhead types, different ink types, or different operating conditions, for example.